Lipid analogs for treating viral infections

ABSTRACT

A method of treating viral infections, and in particular HIV-1, hepatitis B virus, and herpes virus, is disclosed. The method comprises administering to a subject in need of such treatment an infection-controlling amount of a phospholipid or phospholipid derivative.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 09/412,539, filed Oct. 4, 1999, which is a division of U.S. application Ser. No. 08/793,470, filed May 2, 1997, now U.S. Pat. No. 5,962,437, issued Oct. 5, 1999; which is a 371 of International Application No. PCT/US95/10111, filed Aug. 7, 1995; which is entitled to priority to U.S. application Ser. No. 08/314,901, filed Sep. 29, 1994 and to U.S. application Ser. No. 08/297,416, filed Aug. 29, 1994.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not Applicable.

FIELD OF THE INVENTION

This invention relates generally to the treatment of viral infections, and more specifically to the treatment of viral infections with phospholipids and phospholipid derivatives.

BACKGROUND OF THE INVENTION

A current treatment for combating human immunodeficiency virus type 1 (HIV-1) infections is the administration of the nucleoside analog 3′-azido-3′-deoxythymidine (AZT) to an afflicted subject. See, e.g., U.S. Pat. No. 4,724,232 to Rideout et al. HIV-1 infection treatment methods have also included the administration of ether lipid compounds in an amount effective to inhibit replication of the virus in infected cells, see e.g., Kucera et al., AIDS Research and Human Retroviruses 6:491 (1990), and ether lipids conjugated with AZT and other antiviral nucleoside analogs. See PCT Application No. US91/04289 (published 26 Dec. 1991). These compounds appear to act at the plasma membrane to block the endocytic process of HIV-1 into CD4⁺ cells and the process of virus assembly, cell fusion and pathogenesis. They also can inhibit the activity of protein kinase C. Given the seriousness of HIV-1 infection worldwide, there is an ongoing need for new methods of combating HIV-1 infections.

Another virus of serious concern, hepatitis B virus (HBV), is one of a family of hepadnaviruses that cause acute and chronic liver disease, including liver cancer. HBV, which is found in the body fluids of infected persons, makes three antigenic proteins during multiplication in liver cells: hepatitis B surface antigen (HBsAg), hepatitis B e antigen (HBeAg) and hepatitis B core antigen (HBcAg). These three virus antigenic proteins are important as markers for determining virus infection, as antibodies against the virus infection are made in response to these virus proteins in the blood. An HBV vaccine is available to prevent infection, and hyperimmune gamma globulin is available for temporary prophylaxis against developing HBV infection in persons at risk. Clearly specific antiviral agents are needed for treatment and control of HBV infections in humans.

Based on the foregoing, it is an object of the present invention to provide a new treatment method for combating the effects of HIV-1.

It is another object of the present invention to provide compounds and pharmaceutical compositions for carrying out HIV-1 treatment methods.

It is also an object of the present invention to provide a new treatment method for combating the effects of HBV.

It is a second object of the present invention to provide compounds and pharmaceutical compositions for carrying out HBV treatment methods.

SUMMARY OF THE INVENTION

These and other objects are satisfied by the present invention, which provides methods of combating viral infections. As a first aspect, the present invention provides a method of combating a viral infection in a subject in need of such treatment comprising administering to the subject an effective infection-combating amount of a compound of Formula I or a pharmaceutical salt thereof.

In the compounds of Formula I, R₁ is a branched or unbranched, saturated or unsaturated C₆ to C₁₈ alkyl group optionally substituted from 1 to 5 times with —OH, —COOH, oxo, amine, or substituted or unsubstituted aromatic; X is selected from the group consisting of NHCO, CH₃NCO, CONH, CONCH₃, S, SO, SO₂, O, NH, and NCH₃; R₂ is a branched or unbranched, saturated or unsaturated C₆ to C₁₄ alkyl group optionally substituted from 1 to 5 times with —OH, —COOH, oxo, amine, or substituted or unsubstituted aromatic; Y is selected from the group consisting of NHCO, CH₃NCO, CONH, CONCH₃, S, SO, SO₂, O, NH, and NCH₃; R₆ is a branched or unbranched C₂ to C₆ alkyl group; and R₃, R₄, and R₅ are independently methyl or ethyl, or R₃ and R₄ together form an aliphatic or heterocyclic ring having five or six members and R₅ is methyl or ethyl. Preferred compounds include 1-dodecanamido-2-decyloxypropyl-3-phosphocholine, 1-dodecanamido-2-octyloxypropyl-3-phosphocholine, and 1-dodecanamido-2-dodecyloxypropyl-3-phosphocholine. The method is particularly preferred as a treatment to combat viral infections caused by HIV-1, HBV, and herpes simplex virus. The present invention also includes pharmaceutical compositions comprising a compound of Formula I and a suitable pharmaceutical carrier.

As a second aspect, the present invention includes a method of combating viral infections in a subject in need of such treatment which comprises the administration to such a subject a compound of Formula II or a pharmaceutical salt thereof in an effective infection-combating amount.

In Formula II, the ring structure is optionally substituted from 1 to 3 times with C₁ to C₃ alkyl; R₁ is an unbranched or branched, saturated or unsaturated C₆ to C₂₀ alkyl group; R₂, R₃, and R₄ are independently methyl or ethyl, or R₂ and R₃ together form an aliphatic or heterocyclic ring having five or six members and R₄ is methyl or ethyl; X is selected from the group consisting of NHCO, CH₃NCO, CONH, CONCH₃, S, SO, SO₂, O, NH, and NCH₃; R₅ is a branched or unbranched C₂ to C₆ alkyl group; m is 1 to 3; and n is 0 to 2. Preferred compounds of Formula II are 3-hexadecanamido-cyclohexylphosphocholine and 3-hexadecylthio-cyclohexylphosphocholine. Adminstration of the compounds of Formula II is particularly useful in treating viral infections caused by HIV-1, HBV, and herpesviruses. The present invention also includes pharmaceutical compositions comprising a compound of Formula II and a suitable pharmaceutical carrier.

A third aspect of the present invention is a method of treating viral infections comprising administering to a subject in need of such treatment an effective infection inhibiting amount of a compound of Formula III.

In compounds of Formula III, R₁ is a branched or unbranched, saturated or unsaturated C₆ to C₁₈ alkyl group optionally substituted from 1 to 5 times with —OH, —COOH, oxo, amine, or substituted or unsubstituted aromatic; X is selected from the group consisting of NHCO, CH₃NCO, CONH, CONCH₃, S, SO, SO₂, O, NH, and NCH₃; R₂ is a branched or unbranched, saturated or unsaturated C₆ to C₁₄ alkyl group optionally substituted from 1 to 5 times with —OH, —COOH, oxo, amine, or substituted or unsubstituted aromatic; Y is selected from the group consisting of NHCO, CH₃NCO, CONH, CONCH₃, S, SO, SO₂, O, NH, and NCH₃; and Z is a moiety of the Formula V,

wherein: V is H or N₃;

-   -   W is H or F; or     -   V and W together are a covalent bond; and     -   B is a purinyl moiety of Formula VI

optionally substituted at position 2 with ═O—OH, —SH, —NH₂, or halogen, at position 4 with NH₂ or ═O, at position 6 with Cl, —NH₂, —OH, or C₁–C₃ alkyl, and at position 8 with Br or I; or

-   -   B is a pyrimidinyl moiety of Formula VII

substitued at position 4 with ═O or NH₂ and optionally substituted at position 5 with halogen or C₁–C₃ saturated or unsaturated alkyl optionally substituted 1 to 3 times with halogen.

Pharmaceutical compositions comprising these compounds and a pharmaceutical carrier are also encompassed by the present invention.

A fourth aspect of the invention is a method of inhibiting viral infections comprising administering to a subject in need of such treatment an effective infection-inhibiting amount of a compound of Formula IV.

In the compounds of Formula IV, the ring structure is optionally substituted from 1 to 3 times with C₁ to C₃ alkyl; R₁ is an unbranched or branched, saturated or unsaturated C₆ to C₂₀ alkyl group; X is selected from the group consisting of NHCO, CH₃NCO, CONH, CONCH₃, S, SO, SO₂, O, NH, and NCH₃; m is 1 to 3; n is 0 to 2; and Z is a moiety of the Formula V,

wherein: V is H or N₃;

-   -   W is H or F; or     -   V and W together are a covalent bond; and     -   B is a purinyl moiety of Formula VI

optionally substituted at position 2 with ═O—OH, —SH, —NH₂, or halogen, at position 4 with NH₂ or ═O, at position 6 with Cl, —NH₂, —OH, or C₁–C₃ alkyl, and at position 8 with Br or I; or

-   -   B is a pyrimidinyl moiety of Formula VII

substitued at position 4 with ═O or NH₂ and optionally substituted at position 5 with halogen or C₁–C₃ saturated or unsaturated alkyl optionally substituted 1 to 3 times with halogen.

The present invention also includes pharmaceutical compositions comprising a compound of Formula IV and a suitable pharmaceutical carrier.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “alkyl” is intended to refer to an unbranched or branched alkyl group comprising carbon atoms, such as methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, hexyl, and octyl. The term “pharmaceutical salt” refers to a salt that retains the desired biological activity of the parent compound and does not impart undesired toxicological effects thereto. Examples of such salts are (a) salts formed with cations such as sodium, potassium, NH₄ ⁺, magnesium, calcium polyamines, such as spermine, and spermidine, etc.; (b) acid addition salts formed with inorganic acids, for example hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, nitric acid and the like; (c) salts formed with organic acids such as, for example, acetic acid, oxalic acid, tartaric acid, succinic acid, maleic acid, fumaric acid, gluconic acid, citric acid, malic acid, ascorbic acid, benzoic acid, tannic acid, palmitic acid, alginic acid, polyglutamic acid, naphthalenesulfonic acid, methanesulfonic acid, p-toluenesulfonic acid, naphthalenedisulfonic acid, polygalacturonic acid, and the like; and (d) salts formed from elemental anions such as chlorine, bromine, and iodine.

A first aspect of the present invention is a method of combating viral infection comprising administering a compound of Formula I, wherein R₁, R₂, R₃, R₄, R₅, R₆, X, and Y are defined as stated above, or a pharmaceutical salt thereof. The amphipathic compounds of Formula I, which are generally analogs of phosphatidylcholine, include a glycerol backbone (represented by the chain of three carbon atoms to which other functional groups are bonded), lipophilic moieties (represented by R₁ and R₂) bonded to positions 1 and 2 of the glycerol backbone through functional groups (represented by X and Y) that are generally resistant to phospholipase degradation, and polar phosphate and quaternary amine groups (linked to one another through a short alkyl group) bonded to position 3 of the glycerol backbone. Each of these components of the compounds of Formula I is described separately below.

In Formula I, as described above, R₁ is a lipophilic moiety; the lipophilicity of R₁ allows the compounds of Formula I to bind with the cell membrane of a cell infected with a retrovirus to provide an anchor thereto. R₁ can be an unbranched or branched, saturated or unsaturated C₆ to C₁₈ alkyl group. Preferably, R₁ is an unbranched saturated or unsaturated C₈ to C₁₂ alkyl group, and more preferably, R₁ is an unbranched saturated C₁₀ or C₁₂ alkyl group.

In compounds of Formula I, X is a functional group that links the lipophilic moiety R₁ and the glycerol backbone of the compound. X is selected from the group consisting of NHCO, CH₃NCO, CONH, CONCH₃, S, SO, SO₂, O, NH, and NCH₃; these functional groups are resistant to the hydrolytic activity of cellular lipases, in particular phospholipase A, which is specific for ester linkages at position 1 (as are present in phosphatidyl choline). Preferably, X is S or NHCO, with NHCO being most preferred.

In Formula I, R₂ is a lipophilic moiety which, as is true for R₁, enables the compounds of Formula I to bind with the cell membrane of an infected cell. R₂ can be an unbranched or branched, saturated or unsaturated C₆ to C₁₄ alkyl group. Preferably, R₂ is an unbranched saturated or unsaturated C₈ to C₁₂ alkyl group, and more preferably, R₂ is an unbranched saturated C₈ or C₁₀ alkyl group. It is also preferred that R₁ and R₂ together contain between 18 and 22 carbon atoms.

R₂ is bonded to position 2 of the glycerol backbone through a functional group Y, which is selected from the group consisting of NHCO, CH₃NCO, CONH, CONCH₃, S, SO, SO₂, O, NH, and NCH₃. Like X, Y should be a moiety that is resistant to the hydrolytic activity of cellular lipases, and in particular phospholipase B, as this enzyme is specific for ester linkages at position 2. Preferably, X is S or O, with O being more preferred.

The polar hydrophilic end of the amphipathic compounds of Formula I, which can play a role in membrane interaction, comprises an amphoteric phosphoalkyl quaternary amine group in which the phosphate moiety carries the negative charge and the quaternary amine moiety carries the positive charge. In this group, R₆, which is a branched or unbranched, saturated or unsatured C₂ to C₆ alkyl group, is preferably saturated C₂. R₃, R₄, and R₅ are independently selected from the group consisting of methyl and ethyl, with methyl being preferred, and with R₃, R₄, and R₅ each being methyl being more preferred, or R₃ and R₄ together form an aliphatic or heterocyclic ring having five or six members and R₅ is methyl or ethyl.

Exemplary compounds of Formula I include 1-dodecanamido-2-decyloxypropyl-3-phosphocholine (CP-128), 1-dodecanamido-2-octyloxypropyl-3-phosphocholine (CP-130), 1-dodecanamido-2-dodecyloxypropyl-3-phosphocholine (CP-131), and 1-dodecyloxy-2-decyloxypropyl-3-phosphocholine (CP-1 29). These compounds of Formula I can be synthesized according to the procedures set forth in Examples 1 and 2 below. Other compounds of Formula I can be synthesized using the same method with the appropriate reagents substituted for those listed.

Another aspect of the invention is a method of combating viral infection by administering compounds of Formula II, wherein R₁, R₂, R₃, R₄, R₅, X, m, and n are defined as stated above, or a pharmaceutical salt thereof. Compounds of Formula II are amphipathic moieties having a lipophilic moiety (represented by R₁) linked to a five- or six-membered ring structure (which is optionally sustituted 1 to 3 times with C₁ to C₃ alkyl) and a hydrophilic moiety that includes phosphate and quaternary amine groups linked by a short alkyl group that is bonded to the ring structure through the phosphate group. The hydrophilic group is linked to the ring at position 1, and the lipophilic group is linked to the ring at positions 2, 3, or 4. Like the compounds of Formula I, the compounds of Formula II are analogs of phosphatidyl choline. However, the ring structure provides a more conformationally restricted framework for the compound than compounds lacking a ring structure; this restricted framework can provide the compound with more favorable interaction with the cellular membrane and thereby increase its efficacy.

In the compounds of Formula II, R₁ can be an unbranched or branched, saturated or unsaturated C₆ to C₂₀ alkyl group. As with the compounds of Formulas II, R₁ is a lipophilic moiety which binds with the cell membrane of infected cells to provide an anchor thereto. Preferably, R₁ is unbranched saturated or unsaturated C₁₀ to C₁₈ alkyl. More preferably, R₁ is unbranched saturated or unsaturated C₁₆ to C₁₈ alkyl.

In compounds of Formula II, X is a functional group that links the lipophilic moiety R₁ to position 1 of the ring structure. X should be a functional group, such as NHCO, CH₃NCO, CONH, CONCH₃, NH, NCH₃, S, SO, SO₂, or O, that is able to withstand the hydrolytic activity of cellular lipases. Preferably, Y is S or NHCO.

As stated above, the polar hydrophilic end of the amphipathic compounds of Formula II comprises a phosphate group bonded to the ring structure, a short alkyl group R₅ linked at one end thereto, and a quaternary amine group linked to the opposite end of the short alkyl group. R₅ is a saturated or unsaturated, branched or unbranched C₂ to C₆ alkyl group, and is more preferably C₂. R₂, R₃, and R₄ are independently selected from the group consisting of methyl and ethyl, with methyl being preferred, or R₂ and R₃ together form an aliphatic or heterocyclic five- or six-membered ring structure and R₄ is methyl or ethyl. It is more preferred that R₂, R₃, and R₄ are each methyl.

In the compounds of Formula II, m can be 1, 2, or 3, and n can be 0, 1, or 2. Preferably the ring structure is a five- or six-membered ring; thus, preferably m is 2 or 3 when n is 0, m is 1 or 2 when n is 1, and m is 1 when n is 2. As noted above, the ring structure provides conformational rigidity to the compound.

Exemplary compounds of Formula II include 3-hexadecylthio-cyclohexylphosphocholine (INK-1), 3-hexadecanamido-cyclohexylphosphocholine, 3-hexadecanamido-cyclopentylphosphocholine, and 3-hexadecylthio-cyclopentylphosphocholine. These compounds of Formula II can be synthesized by following the teachings of Example 3 below in combination with procedures known to those skilled in the art.

An additional aspect of the present invention is a method of combating viral infection with compounds of Formulas III and IV. These compounds substitute a moiety Z for the alkyl-quaternary amine of the compounds of Formulas I and II, wherein Z is as defined above. Z is a moiety that has demonstrated anti-viral activity by itself; thus conjugation of Z to the remainder of the compounds of Formulas III and IV provides a compound that potentially includes multiple active sites for viral inhibition.

In the compounds of Formula III, R₁, R₂, X and Y are defined above. R₁ is a lipophilic moiety; the lipophilicity of R₁ allows the compounds of Formula I to bind with the cell membrane of a cell infected with a retrovirus to provide an anchor thereto. R₁ can be an unbranched or branched, saturated or unsaturated C₆ to C₁₈ alkyl group. Preferably, R₁ is an unbranched saturated or unsaturated C₈ to C₁₂ alkyl group, and more preferably, R₁ is an unbranched saturated C₁₀ or C₁₂ alkyl group.

In compounds of Formula III, X is a functional group that links the lipophilic moiety R₁ and the glycerol backbone of the compound. X is selected from the group consisting of NHCO, CH₃NCO, CONH, CONCH₃, S, SO, SO₂, O, NH, and NCH₃; these functional groups are resistant to the hydrolytic activity of cellular lipases, in particular phospholipase A, which is specific for ester linkages at position 1 (as are present in phosphatidyl choline). Preferably, X is S or NHCO, with NHCO being most preferred.

In Formula III, R₂ is a lipophilic moiety which, as is true for R₁, enables the compounds of Formula III to bind with the cell membrane of an infected cell. R₂ can be an unbranched or branched, saturated or unsaturated C₆ to C₁₄ alkyl group. Preferably, R₂ is an unbranched saturated or unsaturated C₈ to C₁₂ alkyl group, and more preferably, R₂ is an unbranched saturated C₈ or C₁₀ alkyl group. It is also preferred that R₁ and R₂ together contain between 18 and 22 carbon atoms.

R₂ is bonded to position 2 of the glycerol backbone through a functional group Y, which is selected from the group consisting of NHCO, CH₃NCO, CONH, CONCH₃, S, SO, SO₂, O, NH, and NCH₃. Like X, Y should be a moiety that is resistant to the hydrolytic activity of cellular lipases, and in particular phospholipase B, as this enzyme is specific for ester linkages at position 2. Preferably, X is S or O, with O being more preferred.

In the compounds of Formula III, Z is a moiety of Formula V. Moieties of Formula V are intended to be anti-viral agents, and thus potentially provide an additional active site for anti-viral activity that may act through a different mechanism. In the moieties of Formula V, V is H, or N₃, or V and W together from a covalent bond with H and N₃ being preferred. W is H or F, with H being preferred.

In the compounds of Formula III, B is a purinyl moiety of Formula VI or a pyrimidinyl moiety of Formula VII, each of which are substituted as described above. As used herein, a purinyl moiety comprises six- and five-membered aromatic rings having the molecular structure illustrated in Formula VI. Those skilled in this art will appreciate that the double bonds illustrated in Formula VI are present to represent that the purinyl moieties have aromatic character, and that these double bonds may shift their positions in certain compounds due to the presence of certain substituents to retain the aromatic character of the moiety; in particular, those moieties having ═O or NH₂ substituents at positions 2 and 4, such as adenine, guanine, xanthine, and hypoxanthine, are generally illustrated as having double bonds shifted from the positions shown in Formula VI. Similarly, as used herein a pyrimidinyl moiety comprises a six-membered aromatic ring having the molecular structure illustrated in Formula VII. Those skilled in this art will appreciate that the double bonds illustrated in Formula VII are included therein to represent that the moieties of Formula VII have aromatic character, and that these double bonds may shift for certain substituents, in particular for ═O and NH₂ at positions 2 and 4, in order for the moiety to retain its aromatic character. Preferably, B is selected from the group consisting of adenine, thymine, cytosine, guanine, hypoxanthine, uracil, 5-fluorouracil, 2-fluoro-adenine, 2-chloro-adenine, 2-bromo-adenine, and 2-amino-adenine.

Preferably, Z is 3′-azido-3′-deoxythymidine, dideoxyinosine, dideoxycytidine, or 2′, 3′-didehydro-3′-deoxythymidine. An exemplary preferred compound of Formula III is 3′-azido-3′-deoxy-5′-(3-dodecanamido-2-decyloxypropyl)-phosphothymidine.

A further aspect of the present invention is a method of inhibiting viral infections comprising administering to a subject an effective infection-inhibiting amount of a compound of Formula IV, wherein R₁, R₂, X, m, n, and Z are as defined above. In the compounds of Formula IV, R₁ can be an unbranched or branched, saturated or unsaturated C₆ to C₂₀ alkyl group. As with the compounds of Formula II, R₁ is a lipophilic moiety which binds with the cell membrane of infected cells to provide an anchor thereto. Preferably, R₁ is unbranched saturated or unsaturated C₁₀ to C₁₈ alkyl. More preferably, R₁ is unbranched saturated or unsaturated C₁₆ to C₁₈ alkyl.

In compounds of Formula IV, X is a functional group that links the lipophilic moiety R₁ to position 1 of the ring structure. X should be a functional group, such as NHCO, CH₃NCO, CONH, CONCH₃, NH, NCH₃, S, SO, SO₂, or O, that is able to withstand the hydrolytic activity of cellular lipases. Preferably, X is S or NHCO.

As stated above, the polar hydrophilic end of the amphipathic compounds of Formula IV comprises a phosphate group bonded to the ring structure and a moiety Z as defined in Formula V. In the moieties of Formula V, V is H, or N₃, or V and W together form a covalent bond, with H and N₃ being preferred. W is H or F, with H being preferred.

In the compounds of Formula IV, B is a purinyl moiety of Formula VI or a pyrimidinyl moiety of Formula VII, each of which are substituted as described above. As used herein, a purinyl moiety comprises six- and five-membered aromatic rings having the molecular structure illustrated in Formula VI. Those skilled in this art will appreciate that the double bonds illustrated in Formula VI are present to represent that the purinyl moieties have aromatic character, and that these double bonds may shift their positions in certain compounds due to the presence of certain substituents to retain the aromatic character of the moiety; in particular, those moieties having ═O or NH₂ substituents at positions 2 and 4, such as adenine, guanine, xanthine, and hypoxanthine, are generally illustrated as having double bonds shifted from the positions shown in Formula VI. Similarly, as used herein a pyrimidinyl moiety comprises a six-membered aromatic ring having the molecular structure illustrated in Formula VII. Those skilled in this art will appreciate that the double bonds illustrated in Formula VII are included therein to represent that the moieties of Formula VII have aromatic character, and that these double bonds may shift for certain substituents, in particular for ═O and NH₂ at positions 2 and 4, in order for the moiety to retain its aromatic character. Preferably, B is selected from the group consisting of adenine, thymine, cytosine, guanine, hypoxanthine, uracil, 5-fluorouracil, 2-fluoro-adenine, 2-chloro-adenine, 2-bromo-adenine, and 2-amino-adenine.

Preferably, Z is selected from the group consisting of 3′-azido3′-deoxythymidine, dideoxyinosine, dideoxycytidine, and 2′, 3′-didehydro-3′-deoxythymidine.

In the compounds of Formula IV, m can be 1, 2, or 3, and n can be 0, 1, or 2. Preferably, the ring structure is a five- or six-membered ring; thus m is 2 or 3 when n is 0, m is 1 or 2 when n is 1, and m is 1 when n is 2. The ring structure provides conformational rigidity to the compound.

An exemplary compound of Formula IV is 3′-azido-3′-deoxy-5′-(3-hexadecylthiocyclohexyl)-phosphothymidine.

Experimentation has demonstrated the efficacy of the compounds of Formulas I, II, III and IV in combating viral infection. For example, compounds CP-128, CP-129, CP-130, CP-131, and INK-1 in nanomolar concentration substantially inhibit the HIV-1 activity in CEM-SS cells. Further, these compounds did so at noncytotoxic levels, thus indicating their promise as therapeutic agents for treatment of viral infections. The compounds of Formulas I, II, III and IV are believed to attach to the cell membrane and thus are particularly effective against infections caused by membrane-containing or envelope-containing viruses, as these viruses typically require access to the cell membrane to multiply and assemble through the manufacture of new viral particles. For example, the compounds of Formulas I, II, III and IV can inhibit the transport and/or incorporation of HIV-1 major glycoprotein gp120 in the cell membrane of an infected cell prior to viral assembly. Such inhibition can block the transmission of infectious HIV-1 into neighboring cells. In addition, compounds of Formulas I, II, III and IV can inhibit the production of the HBV core and “e” antigens, each of which contribute to the assembly of new virus particles and the spread of HBV infection. Other infections for which the compounds of Formulas I, II, III and IV should be efficious include those caused by other membrane-containing or envelope-containing herpesviruses, influenza, respiratory syncytial virus, mumps, measles, and parainfluenza viruses.

Experimentation has also shown that the compounds of Formulae I, II, III, and IV have potent anti-tumor activity. In particular, some of these compounds have IC₅₀ values of approximately 1.2 μM against the KB-cell line.

In the manufacture of a medicament according to the invention, hereinafter referred to as a “formulation,” the compounds of Formulas I, II, III and IV are typically admixed with, among other things, an acceptable carrier. The carrier must, of course, be acceptable in the sense of being compatible with any other ingredients in the formulation and must not be deleterious to the patient. The carrier may be a solid or a liquid, or both, and is preferably formulated with the compound as a unit-dose formulation, for example, a tablet, which may contain from 0.5 percent to 95 percent by weight of the active compound. One or more active compounds may be incorporated in the formulations of the invention, which may be prepared by any of the well known techniques of pharmacy consisting essentially of admixing the components.

The formulations of the invention include those suitable for oral, rectal, topical, intrathecal, buccal (e.g., sub-lingual), parenteral (e.g., subcutaneous, intramuscular, intradermal, or intravenous) and transdermal administration, although the most suitable route in any given case will depend on the nature and severity of the condition being treated and on the nature of the particular active compound which is being used.

Formulations suitable for oral administration may be presented in discrete units, such as capsules, cachets, lozenges, or tablets, each containing a predetermined amount of the active compound; as a powder or granules; as a solution or a suspension in an aqueous or nonaqueous liquid; or as an oil-in-water or water-in-oil emulsion. Such formulations may be prepared by any suitable method of pharmacy which includes the step of bringing into association the active compound and a suitable carrier (which may contain one or more accessory ingredients as noted above).

Suitable solid diluents or carriers for the solid oral pharmaceutical dosage unit forms are selected from the group consisting of lipids, carbohydrates, proteins and mineral solids, for example, starch, sucrose, lactose, kaolin, dicalcium phosphate, gelatin, acacia, corn syrup, corn starch, talc and the like.

Capsules, both hard and soft, are filled with compositions of these active ingredients in combination with suitable diluents and excipients, for example, edible oils, talc, calcium carbonate and the like, and also calcium stearate.

In general, the formulations of the invention are prepared by uniformly and intimately admixing the active compound with a liquid or finely divided solid carrier, or both, and then, if necessary, shaping the resulting mixture. For example, a tablet may be prepared by compressing or molding a powder or granules containing the active compound, optionally with one or more accessory ingredients. Compressed tablets may be prepared by compressing, in a suitable machine, the compound in a free-flowing form, such as a powder or granules optionally mixed with a binder, lubricant, inert diluent, and/or surface active/dispersing agent(s). Molded tablets may be made by molding, in a suitable machine, the powdered compound moistened with an inert liquid binder.

Liquid preparations for oral administration are prepared in water or aqueous vehicles which advantageously contain suspending agents, for example, methylcellulose, acacia, polyvinylpyrrolidone, polyvinyl alcohol and the like.

Formulations suitable for buccal (sub-lingual) administration include lozenges comprising the active compound in a flavored base, usually sucrose and acacia or tragacanth; and pastilles comprising the compound in an inert base such as gelatin, glycerin, sucrose, or acacia.

Formulations of the present invention suitable for parenteral administration conveniently comprise sterile aqueous preparations of the active compound, which preparations are preferably isotonic with the blood of the intended recipient. These preparations are preferably administered intravenously, although administration may also be effected by means of subcutaneous, intramuscular, intrathecal, or intradermal injection. The formulation should be sufficiently fluid that for easy parental administration. Such preparations may conveniently be prepared by admixing the compound with water or a glycine buffer and rendering the resulting solution sterile and isotonic with the blood. Such preparations should be stable under the conditions of manufacture and storage, and ordinarily contain in addition to the basic solvent or suspending liquid, preservatives in the nature of bacteriostatic and fungistatic agents, for example, parabens, chlorobutanol, benzyl alcohol, phenol, thimerosal, and the like. In many cases, it is preferable to include osmotically active agents, for example, sugars or sodium chloride in isotonic concentrations. Injectable formulations according to the invention generally contain from 0.1 to 5 percent w/v of active compound and are administered at a rate of 0.1 ml/min/kg.

Formulations suitable for rectal administration are preferably presented as unit dose suppositories. These may be prepared by admixing the active compound with one or more conventional solid carriers, for example, cocoa butter, and then shaping the resulting mixture.

Formulations suitable for topical application to the skin preferably take the form of an ointment, cream, lotion, paste, gel, spray, aerosol, or oil. Carriers which may be used include vaseline, lanolin, polyethylene glycols, alcohols, and combinations of two or more thereof. The active compound is generally present at a concentration of from 0.1 to 15 percent w/w, for example, from 0.5 to 2 percent w/w.

Formulations suitable for transdermal administration may be presented as discrete patches adapted to remain in intimate contact with the epidermis of the recipient for a prolonged period of time. Such patches suitably contain the active compound as an optionally buffered aqueous solution of, for example, 0.1 to 0.2M concentration with respect to the said active compound.

Formulations suitable for transdermal administration may also be delivered by iontophoresis (see, for example, Pharmaceutical Research 3 (6), 318, (1986)) and typically take the form of an optionally buffered aqueous solution of the active compound. Suitable formulations comprise citrate or bis\tris buffer (pH 6) or ethanol/water and contain from 0.1 to 0.2M active ingredient.

The compounds of Formulas I, II, III and IV are administered in an amount sufficient to combat viral infection. The dose can vary depending on the compound selected for administration, the subject, the route of administration, and other factors. Preferably, the compound is administered in an amount of at least 0.1 ng/kg, 1 ng/kg, 0.001 μg/kg or more, and is adminstered in an amount no greater than 0.1 g/kg, 0.01 g/kg, 1 mg/kg, or less.

The invention is illustrated in greater detail in the following nonlimiting examples. In the Examples, “g” means grams, “mg” means milligrams, “μg” means micrograms, “μM” means micromolar, “mL” means milliliters, “° C.” means degrees Celsius, “THF” means tetrahydrofuran, “DMF” means dimethylformamide, “mol” means moles, “mmol” means millimoles, and “psi” means pounds per square inch.

EXAMPLE 1 Preparation of Amidoalkyl Derivatives

The procedure set forth below was used to prepare the following compounds:

(a) 1-dodecanamido-2-decyloxypropyl-3-phosphocholine (CP-128)

(b) 1-dodecanamido-2-octyloxypropyl-3-phosphocholine (CP-130)

(c) 1-dodecanamido-2-dodecyloxypropyl-3-phosphocholine (CP-131)

3-Amino-1,2-propanediol was reacted with lauroyl chloride at room temperature in pyridine and dimethyl formamide. The resulting dodecanamido propanediol was recrystallized from chloroform, then reacted with triphenylmethyl chloride. The tritylated product was recrystallized from hexanes. The C-2 hydroxyl was alkylated by reaction with sodium hydride and the appropriate alkyl bromide in tetrahydrofuran for formation of the ether linkage at C-2 (1-bromodecane for CP-128; 1-bromooctane for CP-130; 1-bromododecane for CP-131). Column chromatography on silica gel with a discontinuous gradient of hexanes:ethyl acetate (95:5 to 80:20) produced the desired 1-dodecanamido-2-alkoxy-3-trityloxypropane. Detritylation with p-toluensulfonic acid in 5:1 methylene chloride:methanol gave product having a free primary hydroxyl after column chromatography (hexanes:ethyl acetate 95:5 to 0:100). Reaction with 2-bromoethyl phosphodichloridate in diethyl ether and pyridine produced the phosphate ester, which was purified on silica gel with chloroform:methanol (100:0 to 2:1). Displacement of the bromide with aqueous trimethylamine in chloroform:isopropanol:dimethyl formamide (3:5:5) gave the final phosphocholine product after column chromatography with chloroform:methanol:ammonium hydroxide (70:35:1 to 70:35:7).

EXAMPLE 2 Preparation of 1-dodecyloxy-2-decyloxypropyl-3-phosphocholine (CP-129)

Isopropylidene glycerol was alkylated using potassium hydroxide and 1-bromododecane in toluene. The resulting ketal was hydrolyzed with hydrochloric acid in methanol, and the diol formed thereby was recrystallized from methanol. The remaining reaction steps (tritylation, alkylation, detritylation, phosphorylation, amination) followed the procedures described above in Example 1 for the alkylamido derivatives.

EXAMPLE 3 Preparation of cis- and trans-3-hexadecylthio-cyclohexylphosphocholine (INK-1)

2-Cyclohexenone (0.14 mol, 13.4 mL) was dissolved in 10 mL of 10 percent sodium hydroxide and 50 mL of THF. An equimolar amount of hexadecyl mercaptan (0.14 mol, 42.9 mL) was added to the unsaturated ketone and the mixture refluxed to produce 3-hexadecylthiocyclohexanone (70 percent yield). This product (5.23 mmol, 1.851 g) was dissolved in methanol and reduced with sodium borohydride (5.23 mmol, 0.199 g) to give a racemic mixture of 3-hexadecylthiocyclohexanol (yield 62 percent; cis:trans ratio 4:1). The phosphorylating agent was prepared by refluxing phosphorus oxychloride (0.65 mol, 60.8 mL) and 2-bromoethanol (0.38 mol, 27.0 mL) in 25 mL of trichloroethylene to produce 2-bromoethyl dichlorophosphate (yield 53 percent). The 3-hexadecylthiocyclohexanol (0.56 mmol, 0.200 g) was dissolved in diethyl ether:THF (2:1) and refluxed with the 2-bromoethyl dichlorophosphate (222 mmol, 0.3 mL) to produce 3-hexadecylthiocyclohexyl phosphoethyl bromide (yield 54 percent). The latter (0.276 mmol, 0.150 g) was dissolved in isopropyl alcohol chloroform:DMF (5:3:5) and heated at 65° C. with trimethylamine (0.042 mol, 2 mL) to produce the desired product, 3-hexadecylthiocyclohexyl-phosphocholine (yield 38 percent).

This procedure can also be used to prepare 3-alkylthio-cyclopentyl derivatives by substituting 2-cyclopentenone.

EXAMPLE 4 Preparation of cis- and trans-3-hexadecanamido-cyclohexylphosphocholine

2-Cyclohexenone is reacted with benzylamine to give 3-benzylaminocyclohexanone. Hydrogenolysis of the benzylamino group then gives 3-aminocyclohexanone. Reaction with hexadecanoyl chloride affords 3-hexadecanamidocyclohexanone, which is then reduced with sodium borohydride to produce a cis/trans mixture of 3-hexadecanamidocyclohexanol. Separation by column chromatography then gives the pure isomers. Reaction with bromoethylphosphodichloridate, then with trimethylamine will produce 3-hexadecanamido-cyclohexylphosphocholine.

Synthesis of the 2- and 4-alkylamido derivatives can be carried out following essentially similar procedures with the substitution of appropriate starting materials.

EXAMPLE 5 Preparation of 3′-azido-3′ deoxy-5′-(dodecanamido-2-decyloxypropyl)-phosphothymidine

3-Dodecanamido-2-decyloxy-propanol was synthesized via the scheme described in Morris-Natschke et al., J. Med. Chem., 29:2114 (1986). This alcohol was phosphorylated with diphenyichiorophosphate in pyridine to give the corresponding phosphate ester. The phenyl groups were then removed via hydrolysis with PtO₂. The phosphatidic acid derivatives were then conjugated to the 5′-hydroxyl of AZT (DCC condensation).

EXAMPLE 6 Preparation of 3′-azido-3′ deoxy-5′-(dodecytoxy-2-decyloxypropyl)-phosphothymidine

A. 3-Dodecyloxy-1,2-propanediol¹

Isopropylidineglycerol (solketal, 26.4 g, 0.20 mol) in 60 mL of toluene was added dropwise to a solution of powdered KOH (22.4 g, 0.04 mol) in 150 mL toluene. The resulting mixture was refluxed for 4 hours. 1-Bromodecane (50 g, 0.20 mol) in 40 mL of toluene was then added dropwise, and the solution was refluxed for 10 hours. After cooling, the reaction mixture was diluted with 200 mL of ice-water and extracted with diethyl ether (3×100 mL). The ether layers were dried over magnesium sulfate, and the solvent was removed in vacuo. The residue was dissolved in 60 mL of diethyl ether and 260 mL of MeOH. Concentrated HCl (60 mL) was added, and the solution was refluxed for 16 hours. After cooling, ice water (150 mL) was added, and the layers were separated. The aqueous layer was extracted with diethyl ether (2×75 mL). The combined organic fractions were then dried over sodium sulfate, filtered, and concentrated in vacuo. The solid residue was recrystallized from MeOH to give 37 g (0.14 mol), 71% of a white solid.

B. 3-Dodecyloxy-1-triphenylmethoxy-2-propanol

The diol synthesized in Section A was tritylated with trityl chloride (59 g, 0.21 mol) in pyridine (200 mL) at 70° C. for 5 hours and then at room temperature overnight. The pyridine was removed under vacuum, and the solid residue was partitioned between water and CHCl₃. The CHCl₃ layer was washed with 5 percent HCl and water, then dried over magnesium sulfate. After removal of solvent, the product was recrystallized from hexanes:ethyl acetate (10:1) to give 19 g of pure product.

C. 3-Dodecyloxy-2-decyloxy-1-triphenylmethoxypropane

The trityl ether of Section B (13.5 g, 0.027 mol) was added dropwise to an ice-cooled suspension of sodium hydride (80%, 1.6 g, 0.054 mol) in 150 mL of tetrahydrofuran under nitrogen. After stirring for 2 hours at room temperature, heat was applied (55° C.). 1-Bromodecane (6 g, 0.027 mol) was added dropwise; heating was continued for 6 hours. After cooling for 3 hours, water was added slowly. Diethyl ether (2×100 mL) was added, and the solution washed with 15 percent sodium thiosulfite, water, and brine. After drying over sodium sulfate, the ether was removed, and the residue was chromatographed with a gradient of hexanes:ethyl acetate (100:0 to 20:1) to give 9 g (52%) of a clear liquid.

D. 3-Dodecyloxy-2-decyloxy-1-propanol

Detritylation of the product of Section C was accomplished using p-toluenesulfonic acid (0.9 g) in CHCl₃:MeOH (72 mL:36 mL) (stirred at room temperature for 48 hours, added 10 percent sodium bicarbonate, extracted with CHCl₃, dried over magnesium sulfate, and concentrated). The residue was purified by column chromatography using a gradient of hexanes:ethyl acetate (20:1 to 5:1) to give 3.5 g (63%) of pure 3-dodecyloxy-2-decyloxy-1-propanol.

E. 3-Dodecyloxy-2-decyloxypropyl Diphenyl Phosphate

Diphenylchlorophosphate (0.7 mL, 3.4 mmol) in 10 mL of diethyl ether was cooled to 4° C. under nitrogen. 3-Dodecyloxy-2-decyloxy-1-propanol (1.0 g, 2.6 mmol) in 15 mL of pyridine and 5 mL of diethyl ether was added. The solution was warmed to room temperature then heated to about 52° C. for 3 hours. It was then cooled to room temperature, diluted with 50 mL of diethyl ether, and washed with water (2×25 mL), 0.5 N HCl (25 mL), and then water (25 mL). The organic layer was dried over sodium sulfate, filtered, and concentrated in vacuo to an oil. Chromatography with a gradient of hexanes:ethyl acetate (10:1 to 1:1) produced 980 mg (1.5 mmol, 60%) of pure product.

F. 3-Dodecyloxy-2-decyloxpropyl Phosphate

PtO₂ (69 mg) was placed in a Parr hydrogenation bottle. The diphenyl phosphate of Section E (500 mg) in 100 mL of EtOH was then added. The reaction mixture was hydrogenated at 15 psi for 1.5 hours until hydrogen uptake ceased. The reaction mixture was then filtered through Celite, and the EtOH was removed in vacuo. The oil was dissolved in 25 mL of pyridine, concentrated in vacuo, and dried under high vacuum to give 350 mg of pure solid phosphatidic acid.

G. 3′-Azido-3′-deoxy-5′-(3-dodecyloxy-2-decyloxypropyl)-phosphothymidine

AZT (43 mg, 0.16 mmol) and the phosphatidic acid of Section F (105 mg, 0.22 mmol) were azeotropically dried with pyridine (3×3 mL) by in vacuo removal. Dicyclohexylcarbodiimide (220 mg, 1.07 mmol) was added, and the drying was repeated 4 times. A final 3 mL portion of pyridine was added, and the reaction mixture was stirred at room temperature in a desiccator for 4 days. Water (1 g) was added, and the mixture was stirred for 4 hours. The solvents were removed in vacuo, and the crude material was chromatographed on 2 g of silica gel using a gradient of CHCl₃:MeOH (15:1 to 2:1). The product was dissolved in 11 mL of CHCl₃:MeOH:H₂O (4:6:1) and stirred with 1.5 g of Whatman preswollen microgranular cation (Na⁺) exchange concentrated in vacuo to give 37 mg of product (22%). FAB ms showed a [MH+Na] ion at 752.4350 (C₃₅H₆₄N₅O₉PNa, 1.4 ppm) and a [M+2Na]⁺ ion at 774.4179 (C₃₅H₆₃N₅O₉PNa₂, 2.0 ppm).

EXAMPLE 7 Procedure for Assessing Anti-HIV-1 Activity

The inhibitory effects of synthetic phospholipid compounds on the replication of human immunodeficiency virus type 1 (HIV-1) virus in cells was examined by the plaque assay procedure of L. Kucera et al., Aids Research and Human Retroviruses 6, 491 (1990). In brief, CEM-SS cell monolayers were infected with HIV-1. Infected cells were overlaid with RPMI-1640 medium plus 10 percent fetal bovine serum (FBS) supplemented with different concentrations of inhibitor. Plaques were counted at five days after infection. In this assay HIV-1 syncytial plaques are seen as large, multicellular foci (10 to 25 nuclei/syncytium) that appear either brown and granular or clear. Since the number of HIV-1 syncytial plaques correlates with reverse transcriptase (RT) and p24 core antigen activity in the HIV-1 infected cell overlay fluids, the syncytial plaque assay can be used to quantify the amount of infectious virus. Reverse transcriptase activity was assayed according to a described procedure (B. J. Poeisz et al., Proc. Natl. Acad. Scie. (U.S.A.) 77, 7415 (1980)). The activity of p24 core antigen induced by HIV-1 infection of CEM-SS cells was measured spectrophotometrically using the commercial Coulter EIA.

EXAMPLE 8 Results of Assessment of Anti-HIV-1 Activity

The results (Table 1) showed that all of the lipid compounds tested have an IC₅₀ against HIV-1 syncytial plaque formation ranging from 0.11 to 0.64 μM. The compounds' IC₅₀ for cell cytotoxicity ranged from 11.85 to 75.7 μM. The highest differential selectivity (611.7), which is a ratio of the cytotoxicity to the anti-HIV-1 activity, was obtained with compound CP-130.

TABLE 1 Evaluation of Ether Lipids for Cytotoxicity and Anti-Viral Activity in CEM-SS Cells IC50 (μM) Differential Compounds Cytotoxicity Anti-HIV-1 Activity Selectivity CP-128 31.6 0.14 225.7 CP-129 75.7 0.64 176.0 CP-130 67.2 0.11 611.7 CP-131 36.6 0.32 114.2 JM-1 (cis) 11.85 0.42 28.2

-   Cytotoxicity was measured by uptake of TdR-H³ into total DNA in the     presence of serial concentrations of compound. -   Anti-HIV-1 activity was measured by standard plaque assay using     CEM-SS cell monolayers. -   Differential selectivity was determined by dividing the IC50 for     cytotoxicity by the IC50 for anti-HIV-1 activity.

EXAMPLE 9 Assessment of HBV Activity Inhibition

Human hepatoblastomas (HepG2) cells were tranfected with plasmid DNA containing tandem copies of HBV genomes. These cells constituitively replicate HBV particles. HepG2 cells were treated with varying concentrations of CP-128 to determine the toxic cell concentration (TC₅₀) by neutral red dye uptake. Also, the inhibitory concentration (IC₅₀) of CP-128 for HBV replication was determined by ELISA.

It was determined that CP-128 cytotoxicity (TC₅₀) was 61.7 μM and the anti-HIV-1 activity (IC₅₀) was 15.6 μM (Table 1). These data indicate that CP-128 has selective anti-HBV activity. Mechanism studies indicate that CP-128 can have an inhibitory effect on the cellular production of HBV-induced DNA, core antigen (HBcAg) and “e” antigen (HBeAg). As a result, it is postulated that CP-128 and other compounds of the present invention are likely inhibiting the assembly of HBV nucleocapids and the packaging of viral pregenomic DNA.

The foregoing examples are illustrative of the present invention and are not to be construed as limiting thereof. The invention is defined by the following claims, with equivalents of the claims to be included therein. 

1. A compound of formula I:

wherein: R₁ is a branched or unbranched, saturated or unsaturated C₆ to C₁₈ alkyl group; X is selected from the group consisting of —NHC(O)— and —S—; R₂ is a branched or unbranched, saturated or unsaturated C₆ to C₁₄ alkyl group; Y is selected from the group consisting of —O— and, —S—; and R₃, R₄, and R₅ are each independently methyl or ethyl.
 2. The compound of claim 1, wherein R₁ is an unbranched C₈–C₁₂ alkyl.
 3. The compound of claim 2, wherein R₁ is an unbranched C₁₀–C₁₂ alkyl.
 4. The compound of claim 1, wherein R₂ is an unbranched C₈–C₁₂ alkyl.
 5. The compound of claim 4, wherein R₂ is an unbranched C₁₀–C₁₂ alkyl.
 6. The compound of claim 1, wherein X is —NHC(O) and Y is —O—.
 7. The compound of claim 1, wherein X is —NHC(O) and Y is —S—.
 8. The compound of claim 1, wherein X is —S and Y is —O—.
 9. The compound of claim 1, wherein R₃, R₄, and R₅ are each methyl.
 10. The compound of claim 1, wherein R₁ is a branched or unbranched, saturated or unsaturated C₆ to C₁₈ alkyl group; X is —NHC(O)—; R₂ is a branched or unbranched, saturated or unsaturated C₈ to C₁₂ alkyl group; Y is —O— and; R₃, R₄, and R₅ are each independently methyl or ethyl.
 11. The compound of claim 10, wherein R₃, R₄, and R₅ are each methyl.
 12. The compound of claim 1, wherein R₁ is a branched or unbranched, saturated or unsaturated C₆ to C₁₈ alkyl group; X is —NHC(O)—; R₂ is a branched or unbranched, saturated or unsaturated C₁₀ to C₁₂ alkyl group; Y is —O— and; R₃, R₄, and R₅ are each independently methyl or ethyl.
 13. The compound of claim 12, wherein R₃, R₄, and R₅ are each methyl.
 14. The compound of claim 1, wherein R₁ is a branched or unbranched, saturated or unsaturated C₈ to C₁₂ alkyl group; X is —NHC(O)—; R₂ is a branched or unbranched, saturated or unsaturated C₆ to C₁₄ alkyl group; Y is —O— and; R₃, R₄, and R₅ are each independently methyl or ethyl.
 15. The compound of claim 14, wherein R₃, R₄, and R₅ are each methyl.
 16. The compound of claim 1, wherein R₁ is a branched or unbranched, saturated or unsaturated C₁₀ to C₁₂ alkyl group; X is —NHC(O)—; R₂ is a branched or unbranched, saturated or unsaturated C₆ to C₁₄ alkyl group; Y is —O— and; R₃, R₄, and R₅ are each independently methyl or ethyl.
 17. The compound of claim 16, wherein R₃, R₄, and R₅ are each methyl.
 18. The compound of claim 1, wherein R₁ is —(CH₂)₈—CH₃; X is —NHC(O)—; R₂ is —(CH₂)₉—CH₃; Y is —O—; and R₃, R₄, and R₅ are each methyl. 